This invention relates to seals for rotating apparatus, such as centrifuges for preventing liquid or gas flow across the seals. More particularly, the invention relates to a floating seal arrangement especially useful for centrifugal separators but also capable of providing fluid-tight sealing function between relatively rotating elements in various rotating vessels, centrifuges, extractors, chambers and related rotating apparatus.
In the design of such rotating apparatus, in which liquid must be prevented from leaking when transferred through passages as from one chamber to another, or from a rotating vessel to a nonrotating passage, various seal designs have been used for maintaining a fluid-tight relationship between apparatus portions, i.e., assemblies, which rotate relative to one another within such assemblies. For example, in centrifugal separators of the type which separate immiscible liquids into distinct constituents of different specific gravities, such as whole milk into a low butterfat-containing portion and a high-butterfat portion, it is typical to employ gas-tight, liquid-tight assemblies having relatively complex seals. Such seals have often required the use of springs, or various other pre-loading mechanisms, for urging the seals into continuous contact with their associated seats for maintaining the sealing relationship. Such seal assemblies typically are to be lubricated by the liquid flowing through the seal assembly. However, if the flow of liquid through the machine should be cut off, then the seals will operate without sufficient lubrication. That is, they will run, in effect, under "dry," unlubricated conditions. In such a liquid separator, if there is termination of liquid from friction of the seal, preloading can very quickly cause the seal to be destroyed by heat and wear.
For these reasons, it has been a known design practice to incorporate means for providing auxiliary lubrication for protecting the seals when the machine is being started and stopped or product flow is interrupted. In such centrifugal separators, start-up may require several minutes (e.g., 8-10 min.) to reach operational angular velocity (e.g., 5000 rpm) and even longer intervals (e.g., 20-30 min.) to stop. For example, water cooling and lubrication protection systems have been used but these are complicated, expensive and undesirable for various other reasons. E.g., for milk separators, auxiliary water protection systems have been used but require tell-tale flow and other cumbersome means for preventing inadvertent mixture of water with milk product streams.
Accordingly, among the several objects of the invention may be noted the provision of improved sealing arrangement for providing fluid-tight sealing for rotating vessels, contrifuges, extractors, chambers and like fluid-handling apparatus; which does not require for the apparatus means for preloading of seals against their seats; which does not require auxiliary liquid or other means cooling or lubricating of the seals for start-up and shut-down or in the event of an interrupt of liquid product from relative to the apparatus and yet which ensures against seal failure during start-up, shut-down or such product interruption; which greatly minimizes seal wear during operation; which provides such apparatus with freedom from seal replacement for much larger periods then heretofore; which enhances sanitation and in-place cleaning of such apparatus; which eliminates problems associated with use of auxiliary seal liquid and its disposal problems; which provides a sealing action characterized by a free-floating motion of seals which allows both lateral and vertical motion of associated rotating portions of the apparatus, such as a centrifuge vessel, without seal damage; which is particularly useful for apparatus handling liquids or fluids in general which have intrinsic lubricating properties; which allows for problem-free operation during lengthy start-up and shut-down modes, as typical of centrifugal separators and extractors; and which is of extremely simple, reliable, and economical design for simplifying the construction, assembly, disassembly and maintenance of the apparatus in which it is employed. It is a related object of the present invention to provide improved rotating apparatus using such sealing arrangement, and specifically, a centrifugal separator manifesting the foregoing characteristics while having various other advantages of great commercial significance.
Briefly, rotating fluid-handling apparatus to which the invention relates has at least first and second elements which rotate relative to the other about a common axis. In accordance with the invention, a seal assembly provides fluid-tight sealing between the elements. The elements each include passages defining between them communication for fluid flow from one element to the other. The seal assembly comprises at least one annular seat carried by one of the elements coaxially with the axis, the other of the elements defining a chamber in proximity to the seat. The chamber carries within it at least one annular seal coaxial with the axis The seal is fluid-actuated. That is, it is shiftable axially within the chamber between a first position, in which the seal is out of sealing contact with the seat, and a second position, in which the seal is in sealing contact with the seat over an annular sealing surface area. The seal and chamber are mutually configured for causing fluid flow from one element to the other through the passages for producing shifting of the seal from the first position to the second position to cause the sealing surface area to be maintained in fluid-tight, fluid-lubricated relationship with the seat in response to pressure produced by the fluid when flowing from one element to the other during relative rotation of the elements, but for permitting shifting of the seal to the second position in the absence of said pressure, whereby to avoid fluid-unlubricated contact of the seal with the seat.
Other objects will be in part apparent and in part pointed out in the following description.